One type of conventional integrated circuit (IC) package contains an IC, where bonding pads on the IC are generally along its periphery. The bonding pads are connected to a leadframe using wire bonding, and the IC and leadframe are sealed within a plastic or ceramic body. Leads from the leadframe extend from edges of the body and are either soldered to pads of a printed circuit board (PCB) or the leads are pushed into a socket.
A relatively recent trend in IC packaging is called chip-scale packaging. In chip-scale packaging, the IC's bonding pads align with ball sites in a standard ball grid array. The ball site pitch is typically 0.3 mm or 0.5 mm. The IC pads are directly bonded to pads on a PCB, with the substrate of the IC facing upward, so no leadframe is needed. The IC pads are bonded to PCB pads either through ultrasonic welding or solder (using solder balls). In chip-scale packaging, since there is no leadframe, the footprint of the IC on the PCB is a minimum. In this way, the PCB may be very densely packed with ICs, which is desirable in compact applications such as cell phones.
Such chip-scale packaging also simplifies the customer's assembly requirements since all ICs have pads that align with locations on a single type of grid. The PCB contains interconnections between the PCB pads and connects certain pads to PCB connectors.
There are many ICs specifically designed for connection to a leadframes. It would be desirable to convert such existing IC designs to a chip-scale package without a major redesign of the chip and without adversely affecting the performance of the IC.